An optical read/write apparatus is known from European Patent EP 508 522. The requirements imposed on the processing of the low frequency components and the high frequency components of the detected signal differ substantially. The position of the detector and the alignment of the optical system are controlled by a control signal derived from the low frequency components of the detected signal. For this, an accurate and offset-free amplification are important. For the high frequency components, from which the information signal is derived, a comparatively large bandwidth and a relatively constant group delay are required. The European Patent proposes an optical read/write apparatus in which, the high frequency components and the low frequency components are separated from one another by a filter having a resistor arranged between the common input terminal and the first input terminal; and having a capacitor arranged between the first input terminal and the second input terminal. Subsequently, the high frequency components and the low frequency components are processed separately.
U.S. Pat. No. 4,663,749 describes an optical read/write apparatus in which the low frequency components are amplified by a current amplifier whose input current also constitutes the bias current, as a result of which, an offset-free low frequency amplification is achieved. The high frequency signals are processed by a separate amplifier.
JP 12-79428 describes an optical read/write apparatus in which, signals from photodetectors are separated into high frequency components, and low frequency components and are subsequently amplified by operational amplifiers. The amplified low frequency signal is recombined with the high frequency signal.
U.S. Pat. No. 4,785,441 describes apparatus for achieving a reliable tracking in an optical read/write system. In this system the high frequency components are also processed separately from the low frequency components.
The above citations are hereby incorporated herein in whole be reference.